1. Field of the Invention
The subject invention relates to an air conditioning system for a vehicle, frequently referred to as a heating, ventilating and air conditioning (HVAC) system.
2. Description of the Prior Art
Such systems typically include a compressor for compressing a refrigerant, a condenser for condensing the refrigerant, an evaporator for evaporating the refrigerant, a discharge fluid line interconnecting the compressor and the condenser, a liquid fluid line interconnecting the evaporator and the condenser, and a suction fluid line interconnecting the evaporator and the compressor. Also, such systems utilize various valve arrangements for controlling flow through the system during operation and during shutdown and/or in response to a leak of refrigerant in the system. In addition, an accumulator/dehydrator is frequently disposed in the suction line for accumulating refrigerant.
As is known and supported by test data, refrigerant oil reduces refrigerant emissions from components in the compressor. More specifically, polymers and rubber components, such as lip seals and O-rings, exhibit significant reduction in refrigerant permeation and leakage when these components are coated with a film of oil. Such has been recognized in U.S. Pat. No. 3,738,118 to Jacobs.
In a pressure vessel that contains microscopic leak paths, refrigerant under pressure eventually displaces oil molecules in these leak paths. The pressure vessel develops a leak rate that is substantially higher than the leak rate when such leak paths are blocked with oil.
Consequently, the absence of refrigerant oil may also result in high rates of refrigerant emission. The phenomenon of “oil migration” can result in the complete absence of oil in the compressor. Should oil migration, which is dependent on thermal cycling, be permitted to continue for several thermal cycles, the compressor may be completely flushed of oil and emit refrigerant at a rate higher than when the compressor components are coated with oil.
During initial startup of variable compressors, very little oil returns to the rotating lip seal. This is due to the fact that very little suction gas (with oil) enters the crankcase where the rotating seal is located. Therefore, oil return does not occur until the compressor destrokes or cycles allowing the suction gas with oil to flow through the crankcase onto the rotating seal.